Broken spark plug

there is a tool called an easy-out that you may be able to find at Sears, or if you know any local hardware stores go there and ask. Its basically a tapered drill bit that grips and helps you back things out. Since it is a bit and you are working with metal and an opening to the engine just be careful not to drop any metal or porcelain into the spark plug hole

if its the porcelin only the shaft nut will work .if shaft nut is sheared then use an easy out